Phosphate treatment composition for iron and steel products



s 192 07s PHOSPHATE TREATMEM COWOSITION FOR IRON AND STEEL rnonuc'rs Albert L. Kimmel, Leawood, Kane, assignor to Marsh Steel & Aluminum Co., North Kansas City, Mo., a corporation of Missouri 1 No Drawing. Filed Sept. 10, 1962, Ser. No. 222,685

4 Claims. (Cl. 1486.16)

This invention relates to a composition for converting rust on the surface of ferrous products and for conditioning the surface to render the same relatively rust resistant, capable of being painted or worked without subsequent treating steps being required, and presenting a desirable blue-black appearance approximating that of newly processed ferrous materials prior to rusting of the same. The treating composition includes ingredients that cooperate to' convert the rust on the surface of an iron .or steel product, to a modified phosphate film tightly bonded to the ferrous material and which not only resists subsequent rusting,-but presents a very good base .for'

paint, does not interfere with welding or other handling of the iron or steel product, and is of the desired blueblack color of newly processed iron and steel materials.

.fore the protective coating can be applied. Iron and steel materials rust 'rapidlyin the air, particularly under high humidity conditions or when exposed directly to moisture, and therefore many prior proposals have been made concerning treatment compositions for removing rust from iron and steel, and to protect such surfaces against subsequent rusting until a protective coating or the like may be applied directly thereto. These prior compositions have suffered from many inherent defects however, including the cost of the ingredients of the composition, the fact that in many instances rust was removed from the surface, but without a protective coating being left on the material to preclude subsequent rapid rusting thereof, actual removal of the rust but with a material beingleft on the surface of the metal that hastened oxidation thereof unless the treatment composition was rapidly removed from the ferrous product, the necessity of using some kind of scraping operation prior to application of the treatment composition to the iron or steel to remove a major proportion of the rust thereon, imposing serious limitations on the subsequent work ability of the product, or immediate paintability of the same without subsequent treatment of the surface of the ferrous material, and special treatment conditions required to satisfy the special properties of the treatment composition. For example, one widely used method of removing rust from iron and steel products, is to dip the ferrous materials into a pickling tank of hydrochloric acid or a similar strong acid solution, whereby the rust is rapidly removed exposing the bare surface of the,

metal. However, pickling solutions required immediate rinsing of the iron and steel after removal of the same ,from the bath, because the acid reacts with the ferrous material to cause very rapid subsequent oxidation of the product in the absence of complete removal of the acid therefrom. Even if the rinsing operation is carried United States Patent 3,l2,?5 Patented June 29, 1965 "ice like, involved the utilization of phosphorous containing compounds which would react chemically with the iron oxide on the surfaceof the metal, to provide a phosphate film over the ferrous material. Phosphoric acid was found to be the most suitable material for converting the rusty surface to the desired phosphate film, but it has subsequently been determined that a film produced solely by the utilization of phosphoric acid is too porous and does not serve as a truly effective agent retarding subsequent rusting of the material and also providing a firm base for a protective coating subsequently applied to the metal product. In an attempt to overcome the porous nature offthe phosphate coating on the metal produced by the phosphoric acid, various modifiers were incorporated into the treatment composition but defects still existed, not only in the coating, but also in the application procedures required to effectively remove rust from the surface of the-metal, and replace the rust with a fully protective film which not only precluded subsequent rusting of the ferrous product, but also provided a firm base for protective paints or the like. Also it was oftentimes found that a white deposit remained on the material after the treatment thereof with the phosphoric acid composition, and/this detracted from the appearance of the product and also raised questions as to the actual bond of the protective coating to the metal surface. 1

It is therefore the primary object of the present invention to overcome the problems'set forth briefly above, and to permit the treatment of rusty ferrous products so as to convert the rust to a protective film on the material that is of blue-black appearance similar to the original color of the metal, provides an eflective base for protective coatings subsequently applied thereto, and does not in any way interfere with the workability of the product including drawing, forging and welding thereof.

It is another especially significant object of the present invention to provide a treatment composition adapted to form a modified phosphate film on the outer surface of an initially rusty ferrous product and employing only a single solution which can be applied to the metal product in an inexpensive manner, and absolutely precluding the necessity of carrying out subsequent treatment operations or processes to inhibit subsequent rusting, or place the metal in condition for coating with a protective material or for further working or welding thereof.

It is also an important object of the invention to provide a treatment composition for ferrous products wherein the appearance of the surface of the metal subsequent to the treatment, very closely conforms to the original color of the metal at the time of production thereof, and eifectively retains such appearance over an extended period notwithstanding exposure of the metal to the atmosphere even under relatively humid conditions.

Also an important object of the invention is the provision of a treatment composition for rusted ferrous products wherein the composition has suflicient penetrating power to permit treatment of heavily rusted materials without the necessity of initially removing the rusty scale from the product prior to application of the treatment composition to the metal.

of theproduct at a competitive price to prior composi-' tions whichare not as effective as the rust removing and surface conditioning composition disclosed herein.

It is desirable that the treatment composition be in v liquid form so that ferrous'products can be treated by either, dipping the same in a bath of the treatment liquid,

7 or thecomposition applied ,to the surfaces of the metal a tightly knit, relatively nonporous, blue-black film bonded to the surface of the metal and resistant to subsequent oxidation while providing an effective base for various types of protective coatings such as paint. The

.chromate-phosphate film does not in any way interfere with subsequent working or welding of the steel and the protective material may be applied to the metal at a subsequent time without additional surface preparation of the metal being needed. The wetting agent in the treatme'nt composition is present in a predetermined proportion suflicient to effect uniform wetting of the surface of i the product with the treatment composition, but without permitting substantial rew'etting' of the surface of the treated metal product with water'after conversion of the rust to the phosphate-chromate film.

It has been determined that the specifications above canbest be met by combining certain critical chemicals in relatively critical'proportions and diluted with a specified amount of water. The materials giving the desired result have been found to be phosphoric acid, manganese phosphate, red chromic acid and a wetting agent sold under the trade name of Santomerse E, and incorporated.

into a predetermined amount of Water as a diluent. The formulation including the quantities thereof in-preferred ranges are as follows:

Percent by Ingredient: weight Phosphoric acid (85% grade) 40 to 42 Manganese phosphate 0.2 to 0.3 Red chromic acid 0.24 to 0.3 Santomerse E a about 0.24 Water Q.s.

Best results have been obtained by utilizing a composition of the following formulation:

, Percent by Ingredient: weight Phosphoricv acid (85% grade) 40.1 Manganese phosphate 0.24 Red chromic acid 0.02

Santomerse E 0.24

Water- 59.4

Santomerse E is a surface active or wetting agent manufactured and sold by Monsanto Chemical Company, St. Louis, Missouri, and is a detergent of the alkyl aryl sulfonate type. The commercially available composition contains from 25% to 100% active ingredient in combination with an inorganic, inert salt and is identified as a highly active, water soluble, sodium alkyl aryl sulfonate -wherein the alkyl portion has a side chain of more than 1 but less than-10 carbon atoms and the aryl group is chosen from benzene or naphthalene radicals.

In preparation of the treatment composition, the ingredients are added in the order of phosphoric acid, manganese phosphate, Santomerse E and red chromic acid, with constant agitation of the liquid as the materials .are added.

The treatment composition set forth :above may be ap- 4* plied to a ferrous product to remove rust therefrom and provide a phosphate-chromate crystalline film on the material by either dipping the product in a bath of the treatment composition, or spraying or brushing the liquid directly onto the metal surface. The treatment composition should be applied at fullstrength regardless of the application method, and it has been determined that best results are obtained by maintaining the liquid at a temperature between about 70 F. and approximately 180 F. At lower temperatures, the conditioning action of the metal surface is much slower and may not be complete in every instance, whereas at higher temperatures, the treating action is more rapid, but relatively fast evaporation takes place and a second application of the treatment material may be required.

Treatment of steel oriron products by the dipping procedure simply involves immersing the metal in a quantity of. the treatment liquid and for a sufficient time to permit the composition to completely penetrate the coating of rust to the unoxidized area of the metal. The treated products may then be removd from the dip tank and permitted to dry in the air, which normally takes about one .hour. I v

The treating composition may also be brushed onto the rusty iron. or steel, but it is important that a sufficient amount of the liquid be applied to the metal to thoroughly and uniformly wet the surface thereof. Very heavy 'rusted areas should be given a second .coat to assure penetration to the base metal. The iron or steel is then allowed to dry in the air, with normally about one hour being required at 70 F. and 50% relative humidity.

The solution may also be sprayed onto the metal surface to be treated, if the application can be conducted in a well ventilated area. As with the brush application procedure, the rusty surface must be thoroughly wetted 'with the treatment composition to assure penetration of the material to the base metal. Drying time-in this type of application is essentially as with dipping and brushing proceduresas previously explained.

The phosphoric acid ingredient of the treatment compositionattacks the rust on the surface of a ferrous product and converts the iron oxide toferric phosphate. The phosphoric acid also attacks the iron or steel to a limited extent liberating a small amount of hydrogen gas. This gassing is useful in that it-helps to remove loose, thin rust and scale so that initial de-scaling of heavy deposits of rust is not required. Inasmuch as the ferric phosphate film formed on the steel or iron surface during treatment is of relatively porous nature and would not effectively protect the metal or provide a good base for protective coatings, the manganese phosphate combines with the iron oxide and the phosphoric acid to provide a manganese phosphate film that reduces the porosity of the ferric phosphate. Thus, the surface of the treated steel is protected with an iron-manganese phosphate coating. However, to control the color of the coating on the iron or steel and to further enhancethe protective value of the phosphate coating, a chromate complexing agent in the nature of GO-redchromic acid is included in the formulation. The

chromic acid complexes with the iron-manganese phosphate to form a chro'mate-phosphate film over the steel or iron which presents a closeknit, relatively nonporous crystalline film firmly bonded to the base metal and which provides a rust resistant coating over the ferrous product. The crystalline film serves as a particularly effective base for protective coatings such as paintor the like, and also improves the paint adhesion and materially extends the protective life of the coating. 'The complex phosphate film also serves to retain forming oils and similar mate-. rials to improve deep drawing operations, but does not in any way impair subsequent welding, bending or forming of the ferrous material.

The critical surfactantincorporated into the formulation serves the purpose of causing the solution to rapidly wet the ferrous product through the rust coating and down to the base metal, but without retention of sufiicient wetting agent on the film after drying thereof, to cause excessive rewetting of the metal if the same becomes exposed to water. Also, the specific surface active agent of the present formulation is compatible with the other ingredients 'of the liquid and is not destroyed or materially inhibited by the phosphoric acid or the red chromic acid.

The concentrations of the various ingredients are critical in that if the solution is too dilute, it has been determined that the finish on the metal appears mottled and has a gray-green color rather than the desired blue-black appearance. On the other hand, if the solution is too concentrated and the ingredients are present in excessive amounts, the treatment composition does not drain properly from the steel and leaves a very heavy crystalline deposit thereon upon drying of the material and imparting an undesirable greenish blue color to the treated surface. It has also been determined that if an excessive amount of red chromic acid is used, the compound destroys the wetting agent While a deficiency of the chromic acid results in insufiicient chromate ions to properly com- The treatment composition gives the iron or steel product a new-looking appearance by its suface conversion action and further corrosion is effectively inhibited. Improved paint adhesion to the steel is assured and the protective life of the paint system is materially increased.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A composition for treating the surface of a ferrous product consisting essentially of the combination of, calculated as percent by weight, from about 40% to approximately 42% phosphoric acid (85 grade), from about 0.2% to approximately 0.3 manganese phosphate, from about 0.24% to approximately 0.3% of a sodium alkyl aryl sulfonate compound wherein the alkyl group has a side chain containing from 1 to carbon atoms and the aryl group is selected from benzene and naphthalene radicals, about 0.02% of red chromic acid and sufiicient water to bring the total amount of ingredients to 100%.

2. A composition for treating the surface of a ferrous product consisting essentially of the combination of, calculated as approximate percent by weight, 40.1% phos- 6 I phoric acid grade), 0.24% manganese phosphate, 0.24% of a sodium alkyl aryl sulfonate compound Wherein the alkyl group has a side chain containing from 1 to 10 carbon atoms and the aryl group is selected from benzene and naphthalene radicals, 0.02% red chromic acid and 59.4% water.

3. A method of converting the rusted surface of a ferrous product to a blue-black appearing crystalline film tightly bonded to the product and without production of a white deposit thereon, said method comprising the steps of applying to said rusted surface of the product, a composition consisting essentially of the combination of, calculated as percent by weight, from about 40% to approximately 42% phosphoric acid (85% grade), from about 0.2% to approximately 0.3% manganese phosphate, from about 0.24% to approximately 0.3% of a sodium alkyl aryl sulfonate compound wherein the alkyl group has a side chain containing from 1 to 10 carbon atoms and the aryl group is selected from benzene and naphthalene radicals, about 0.02% of red chromic acid and sufficient Water to bring the total amount of ingredients to and allowing the composition to dry on the surface of said product.

4. A method of preparing a composition useful for treating the surface of a ferrous product comprising the steps of admixing in serial order, in quantities sufiicient to provide the defined proportions of the specified ingredients calculated as percent by weight, from about 40% V to approximately 42% of phosphoric acid (85 grade), from about 0.2% to approximately 0.3% of a sodium alkyl aryl sulfonate compound wherein the alkyl group has a side chain containing 1 to 10 carbon atoms and the aryl group is selected from benzene and naphthalene radicals, about 0.02% of red chromic acid and sufiicient waterto bring the total amount of ingredients to 100%; and continuously agitating the admixture during serial addition of said ingredients.

References Cited by the Examiner UNITED STATES PATENTS 2,348,698 5/44 Thompson 1486.l6 2,418,608 4/ 47 Thompson 1'486.16 3,097,118 7/63 Leonard 148-616 X FOREIGN PATENTS 517,916 2/40 Great Britain.

5 3 0,006 12/40 Great Britain.

516,682 9/55 Canada.

RICHARD D. NEVIUS, Primary Examiner.

W. D. MARTIN, Examiner. 

1. A COMPOSITION FOR TREATING THE SURFACE OF A FERROUS PRODUCT CONSISTING ESSENTIALLY OF THE COMBINATION OF, CALCULATED AS PERCENT BY WEIGHT, FROM ABOUT 40% TO APPROXIMATELY 42% PHOSPHORIC ACID (85% GRADE)M, FROM ABOUT 0.2% TO APROXIMATELY 0.3% MANGANESE PHOSPHATE, FROM ABOUT 0.24% TO APPROXIMATELY 0.3% OF A SODIUM ALKYL ARYL SULFONATE COMPOUND WHEREIN THE ALKYL GROUP HAS A SIDE CHAIN CONTAINING FROM 1 TO 10 CARBON ATOMS AND THE ARYL GROUP IS SELECTED FROM BENZENE AND NAPHTHALENE RADICALS, ABOUT 0.02% OF RED CHROMIC ACID AND SUFFICIENT WATER TO BRING THE TOTAL AMOUNT OF INGREDIENT TO 100%. 